Re: [mowbot] The grass keeps getting longer

Dave Everett (deverett nospam at
Thu, 04 Feb 1999 18:49:42 +1100

At 14:02 03-02-99 -0800, you wrote:
>> While I agree that this works fine on level ground, my concern was that
>> inclines can change the COG enough to place it over the unsupported region,
>> or close enough so that if the robot stops, it's inertia would cause it to
>> fall over.
>I'll agree with Robin. By placing the batteries to the rear and as low
>as possible would make it tip back even on a sloped surface. I have flat
>surface anyway, and at a speed of 5 feet per minute (my planned movement
>rate), my inertia will be so low that I don't think it could tip.
If your lawn is failry flat I can't see any problem with that.

>That's why I call a solar only a nipper. It would cut the grass every
>day, so that it would not build up. I have experimented and I can keep
>my loaded wheel drive current below 200 ma, and the unloaded cutter
>motor current under 500 ma.
Mate, no worries if you are drawing such small currents. You've definitely
made the right choices about motors.

>I agree that a weed wacker rips the grass apart. Right now I am leaning
>toward a high power standard blade (only 8" diameter though), with a
>total power consumption of close to 150 watts.
Is that 150w figure correct?
>I guess what I really have to experiment with is my cutting blade. I
>would like to use an 8" diameter blade. 2" of horizontal cutting blade
>on the outside, mounted on a 4" diameter disk. If I spin at 6000 rpm, I
>can let the blades pivot clear if they hit an hard object, and swing
>back out with centrifical force. Now the tough part. I can mill four
>holes in the 4" diameter plate for air passage, and place air scoops to
>force air down in the center, hopefully drawing up air and grass through
>the cutting blades. Another choice is to simply mount a standard 8"
>diameter aircraft prop above the cutting blades but offset at an angle.
>I could mount the cutting blades at an angle to act as a prop, but I
>what the cutting surface to be horizontal. I guess it's time to
>experiment again.
I'll be interested to see the results of your experiments. If you take any
photos or have drawings, I'd like to put your experiments on the website
when they are complete.